Model info file: alternative_ftr_set_subn values don't work properly if they contain whitespace

[nawrockie]

If an alternative_ftr_set_subn value contains whitespace it won't work properly because the code that processes those values looks for this regular expression:

vadr.pm::vdr_FeatureInfoValidateAndConvertAlternativeFeatureSetSubstitution()

line 944:

if($subn_val =~ /^(\S+)\.(\d+)$/) { # e.g. "attachment(cds).2"

Fix could be to either validate that these values do not have whitespace and exit with informative error message if they do, or allow whitespace.